Sunday, August 10, 2014

Another great Magic Lantern feature

As those who read my posting know, in addition to the increased functionality that Magic Lantern brings, it also allows us to travel lighter

For those that take long exposures using ND filters, you will most probably calculate the ‘ND shift’. ML can offer some automation via Auto-ETTR, but if you use high ND densities, eg 1000+, Auto-ETTR will likely not get a solution.

Now, thanks to one of the ML coders (David Milligan) we have a new, in-camera, module for the LE photographers.

For those that are interested this is how I use the new module: 

  • Rather than rely on the manufacture's data, calibrate your NDs or ND stack ups. You may find you didn’t need to do this, but it’s worth a one-off check. We’re only looking for ‘measurable’ differences, eg more than 0.5Ev, say; 
  • A simple way to do this is to focus on blank (single colour) surface, eg fill the frame with a wall. In my case with two NDs (1000 and 16) I took the following images on manual:
    • No ND filter (0Ev), Tv =x 
    • ND 16 filter + 4 stop adjustment on x 
    • ND 1000 filter + 10 stop adjustment on x 
    • ND 1000+16 + 14 stop adjustment on x 
  • Load the test images into LR, or eye-ball the histogram on the camera, look at the luminosity histograms and compare the peaks or the right hand side if you use A-ETTR to set the exposure. Note the deltas and, if significant, note the ‘corrected’ ND values, but don’t worry if less than +/- 0.5Ev; 
  • One final adjustment is to ensure that A-ETTR is not allocated to SET, as this conflicts with the ND module, ie move it to double-press; 

  • To use the new ML module it couldn’t be simpler than this: 
    • Focus, compose and set the exposure, either manually of using A-ETTR; 
    • Add on your ND; 
    • Enable the Bulb timer in the ML menu and enter your (corrected) ND filter value, note the new exposure is shown on the LCD screen, and press and hold SET until the ND module initiates its bulb countdown; 
    • Go and have a cup of coffee if you have a long exposure set.

As a final ‘extra’ from me, if you are doing really long exposures you may see ‘light contamination’ through the eye piece: some believe this happens other don’t. On the safe side use Garry’s ‘copyrighted’ ‘DLSR Eye Patch’; which is made from a piece of black fabric and a Velcro strip. It fits any DSLR, even non-Canon ones! Free user rights to friends :-o)

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